Proposed new patio will be 10m x 3m along the back of the house. I am taking the finish level of the patio from a surface drain that catches rain water from a down pipe.
The top of this drain sits 120mm below the damp course and I intend to set the finish level of the patio 10mm above the drain, so 110mm below damp course.
I understand 150mm is the recommended finish level below damp course but I am working with what I've got.
The drain and pipe joint is set in concrete with the top of the concrete being 190mm below damp course. This gives me 80mm for bedding and slab around the drain, which I believe is sufficient.
The SW pipe (110mm diameter orange hard plastic) sits in pea shingle along the full run from the drain along the side of the house gradually falling to 300mm below damp course at the patio doors where it joins another pipe (90 degree joint) which leads out away from the house under what will be the new patio to a soak away in the garden.
I hope that all makes sense!
When digging down to allow for the 100mm base I have exposed the tops of the pipes in places. In other places (further away from the house) the tops of the pipes are not exposed but are not that far below the surface (about 10-50mm below surface). All pipes are sitting in pea shingle.
Do I need to worry about damaging the pipes when I put down and compact the base?
Is there anything I need to do to ensure the pipes are protected? If so, what is the recommendation? Cover with concrete or maybe put down a dry mix of sharp sand, pea shngle and cement, gentle tamp down and sprinkle with water to harden?
How thick should this be?
After suitably covering the pipes, to bring the base up to bedding level, will it be OK to then put down compacted based on top?
For the pipes that run along the side of the house, there is insufficient depth to put down a 100mm base. Should I cover the pipes with concrete to bring up to the bedding level or would a dry mix of sharp sand, pea shingle and cement also work?
Another question...
I would like to build a step below the patio doors to prevent the long drop down to the patio.
I plan to use house bricks to raise the step with patio slabs used for the tread. The finish height will be half a brick above damp course so as to make it a comfortable step out of the doorway.
The step will be about 2000mm wide with a tread of about 600mm.
Obviously the step needs a solid foundation but I am unsure how best to lay the foundation given the pipes that join below the doorway.
Is it best to lay the foundation on the sub base directly on top of the pipes?
Or on a compacted base layer above the pipes?
Or maybe use the patio itself as a foundation and lay bricks directly on top of the patio?
What thickness should the foundation be if laid on the sub base versus laid on the compact base?
Is it best to use concrete for the foundation or a mortar mix?
Sorry, one more question...
Is crushed concrete 50mm - dust suitable as base? How does it compare to other types of MOT 1?
Appreciate your advice - great site by the way
